1. Field of the Invention
This invention relates generally to the field of information transmission networks and more specifically to Logical Node identification of such networks. More particularly, the present invention relates to Logical Node identification of such networks supporting session based routing/switching of information flow in heterogeneous networks.
2. Description of the Background Art
In the field of information transmission, routing and switching of information to the destination node is most commonly accomplished in one of two approaches: (1) symmetric switched virtual paths/circuits (i.e., ATM) or (2) packet-based routed networks (i.e. Internet). A third type of information routing/switching network exists in many forms that can be better supported through a variant of the two approaches with asymmetric switched virtual paths/circuits or asymmetric packet based routing.
This third area can be classified into two categories: first, the set of information transmission networks that require a combination of the packet routed networks tightly coupled with asymmetric switched networks (i.e. interactive multimedia content delivery such as in video-on-demand that requires a streaming network flow for video and audio and usually an Out Of Band IP network to handle the interactivity between the source and destination); second, the set of information transmission networks that can improve network latency by taking advantage of the knowledge of the point of access in packet based networks (i.e., dynamic routing changes necessary to support unique roving lap top computers). The present application will address this first case.
The former category of information transmission networks is what the present invention will address in detail. In particular, the interactive multimedia service of video-on-demand over Hybrid Fiber Coax (HFC) networks is currently in existence for cable services. In this case, there exists unidirectional content streaming (QAM modulated video and audio streaming of content to the digital set top box in the home) and IP based interactivity (via Out Of Band downstream to the home and a varied Return Path packet forwarding connectivity from the subscriber""s set top box to the cable headend equipment). This same solution can be used for satellite broadcast (content delivery) with wireless (cell phone) or telephone modem for interactivity; as well as for terrestrial broadcast systems (e.g. MMDS, LMDS). It is also noted that the control session via the Out Of Band could also be multiplexed into the streaming link in the In Band.
A technique to increase the number of video-on-demand programs that can be concurrently transmitted is by channel reuse, where programs are assigned to channels at an intermediate node (typically referred to as a xe2x80x9cremote headendxe2x80x9d or xe2x80x9chubxe2x80x9d) where lines from individual subscriber stations are coupled to the main CATV network. For the purposes of the present invention, the term xe2x80x9cheadendxe2x80x9d is defined as any physical site where modulation, demodualtion, and processing (controlling, monitoring, etc.) equipment are kept and operated whether they be staffed with human operators or unstaffed sites that are remotely monitored whether they relate specifically to Cable or other transmission means such as MMDS. This technique allows the same channels to be assigned to different programs at different nodes (known as spectrum reuse through physical media partitioning). Thus, dedicated video-on-demand channels can transmit programs to one set of subscriber stations coupled to a first hub, while the same channels can be used to transmit a different set of programs to another set of subscriber stations coupled to a second hub.
Typically, provision of video-on-demand services is implemented by assigning a session control manager (SCM) to one or more hubs. The SCM is responsible for receiving requests from set-top boxes at associated hubs and providing the requested services. Each SCM must then be informed of the subscriber stations corresponding to the assigned hub. Based on this topological information, the SCM provides the information for the creation of a virtual circuit from the video server to the QAM modulator, and thus an access mechanism to the video and audio stream from the set top box. The SCM also tells the set top box which frequency to tune the demodulator and which packet identification numbers (PIDs) to filter for the video and audio streams.
If subscriber stations are added or deleted, such as by new or canceled subscriptions, then the mapping between SCMs , hubs, and set top boxes may need to change. For example, a set of QAM channels can only accommodate a certain number of subscriber stations. If the number of subscriber stations on a hub exceeds the capacity of the allocated stream, then further Logical Node partitioning may occur on the hub. While such changes can be made to the mapping information in the headend manually, it is desirable to have a more efficient and automated method for re-assigning channels for node usage.
In a principal aspect, the present invention provides automatic transmission to subscriber stations of information about corresponding session control managers and coupling of channel groups defined as nodes.
In accordance with the principles of the present invention, a video-on-demand (VOD) system includes a plurality of session control managers to cause transmission of a requested program to a requesting subscriber station. The video-on-demand system is coupled to a plurality of subscriber stations by a network capable of spectrum reuse between the subscriber station and a corresponding one of a plurality of nodes disposed between the video-on-demand system and the subscriber station. The video-on-demand system comprises a Logical Node assignor which assigns a logical identification to each of the nodes to identify a correspondence between each of the nodes and a corresponding one of the session control managers. For example, a Logical Node for HFC is defined as the group of Fiber Nodes that share the same QAM modulation spectrum i.e. same streams in VOD channels.
In accordance with further aspects of the invention, the Logical Node assignor periodically transmits node assignment information to each of the nodes in the network to uniquely identify the Logical Node and also identify a corresponding session control manager for each of the nodes. This allows for the subscriber stations tune to this digital channel at any time and get these information on a timely basis. Advantageously, such techniques allows automatic dissemination of information regarding mapping between session control managers, Logical Nodes, and subscriber stations. The result is reduced complexity and overhead in managing a video-on-demand system, thereby reducing overall costs.
The principles of the present invention are particularly advantageous in Hybrid Fiber Coaxial (HFC) systems used for transmission of video programming. However, the principles described herein may also be used in direct broadcast satellite (DBS) systems, Local Multi-Point Distribution Services (LMDS), and Multi-channel Multiunit Distribution Systems (MMDS).
One particular advantage of the present invention, is that because of the automatic identification of the Logical Node to which each subscriber station is associated, the present invention allows for switching the unicast VOD stream to the correct QAM modulator that modulates to the Logical Node for receipt by the subscriber station. This is particularly advantageous as new Logical Nodes can be created or existing nodes are divided because of increasing demand for subscription and service.